Mid-Call Synchronization for U-TDOA and AOA Location in UMTS

ABSTRACT

In a wireless location system, a method for determining frame and slot timing information for use in receiving an uplink signal from a user equipment (UE) device assigned to an uplink Dedicated Physical Control Channel (DPCCH) includes receiving signals in the uplink DPCCH at a location measurement unit (LMU) of the WLS. The method also includes detecting a predefined bit pattern known to be present in a plurality of predefined slots of the uplink DPCCH. Next, the frame and slot timing information are determined for the uplink DPCCH based on the detected bit pattern. Finally, the frame and slot timing information is used for collecting uplink signals from the UE for use in location processing.

This application is a continuation of U.S. application Ser. No.11/956,193, filed Dec. 13, 2007, currently pending, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to methods and apparatus forlocating wireless devices, also called mobile stations (MS), such asthose used in analog or digital cellular systems, personalcommunications systems (PCS), enhanced specialized mobile radios(ESMRs), and other types of wireless communications systems. Moreparticularly, but not exclusively, the present invention relates to thediscovery of W-CDMA radio signaling timing while in mid-call, in awireless location system (WLS).

BACKGROUND

A presently preferred implementation of the inventive subject matterdescribed herein is especially suited for synchronization of an uplinktime difference of arrival (U-TDOA) wireless location system, or ahybrid system employing U-TDOA and angle of arrival (AoA) locationtechnologies. Such systems may be used in connection with wirelesscommunication systems employing spread spectrum techniques and rely onthe uplink radio path between a user equipment (UE) device in the activestate and a UMS base station (Node B) for the collection of radiosignals, which are then used for TDOA and/or TDOA/AoA locationcalculations.

Code Division Multiple Access (CDMA) is a now common method fortransmission of voice and data over radio. TruePosition was a pioneer inlocation of CDMA mobiles when in the year 2000, it conducted extensivetesting with Verizon Wireless in mid-town Manhattan, N.Y. VerizonLaboratories used the rigorous test plan published by the CDMADevelopment Group (CDG) to determine the performance of TruePosition'snetwork-based location technology in the challenging urban canyon (10 to25 story buildings) environment. The WLS demonstrated sub-100 meterlocation results in a variety of indoor, outdoor, pedestrian, and movingvehicle scenarios. In the trial, unmodified CDMA (IS-95) mobile phoneswere used to make more than 30,000 test calls. These calls were placedby both Verizon Labs (formerly GTE Labs) and TruePosition in an areacovered by 30 cell sites hosting time difference of arrival (TDOA)receivers.

The inventive techniques and concepts described herein apply tocode-division radio communications systems, including the technologiesreferred to in technical specifications as CDMAOne (TIA/EIA IS-95 CDMAwith IS-95A and IS-95B revisions), CDMA2000 family of radio protocols(as defined by the 3rd Generation Partnership Project 2 (3GPP2)), and inthe Wideband Code-Division Multiple-Access (W-CDMA) radio system definedby the 3rd Generation Partnership Project (3GPP) as part of theUniversal Mobile Telephone System (UMTS). The UMTS model discussedherein is an exemplary but not exclusive environment in which thepresent invention may be used. FIG. 1 depicts exemplary UMTS environmentin which the present invention may be employed. These are explained ingreater detail below.

To date, the UMTS option using the Frequency Division Duplex (FDD mode)of Wideband Code Division Multiple Access (W-CDMA) as the underlying airinterface has been most widely deployed. Frequency Division Duplex isemployed in UMTS to provide an uplink and downlink radio channel betweenthe network and the user. The uplink and downlink frequencies areassigned and use separate spectral bands. FDD UMTS transceivers musttune between the uplink and downlink frequencies to transmit andreceive, respectively. W-CDMA is a direct sequence spread spectrumsystem where base stations are not synchronized. Asynchronous basestations and thus asynchronous radio signaling requires mobile devicesto acquire a timing reference and to synchronize to a base station (aNode B in UMTS) before communications can commence. In a UMTS, FDD,W-CDMA-based, system, the mobile device receives the Broadcast Channel(BC) from the base station (called the Node B in UMTS) to acquire therough timing needed to access the Reverse Access Channel (RACH). Thisacquisition and synchronization procedure is called a “cell search”.

UMTS Frame and Slot Synchronization

In a W-CDMA system, the primary and secondary synchronization downlink(Node B to UE) channels (P-SCH, S-SCH) provide radio frame and time slotsynchronization. The basic unit of time in UMTS radio signals is a 10millisecond (ms) radio frame, which is divided into 15 slots of 2560chips each. UMTS radio signals from a Node B to a UE are “downlinksignals,” while radio signals in the reverse direction are called“uplink signals.” This structure is depicted in FIG. 2 and explained ingreater detail below.

For each UE, initial cell search algorithms are used to synchronize theUE to a Node B. The UE accomplishes this procedure via a common downlinkchannel called the physical synchronization channel (PSCH).

When a UE is first powered on, the UE performs a cell search. In thecell search, the UE looks first for a downlink synchronization channel(SCH). The SCH is a common downlink channel transmitted from the cellallowing UE's within the radio footprint of the cell to synchronize atthe slot and frame levels and to determine the particular scramblingcode group of the cell. As specified in technical specifications for theUMTS standards, the downlink synchronization channel (DL-SCH or justSCH) is a sparse downlink channel that is only active during the first256 chips of each slot. The SCH is made up of two sub-channels, thePrimary SCH (PSCH) and the Secondary SCH (SSCH). The PSCH 256 chipsequence, or PSCH code, is the same in all slots of the SCH for allcells. In contrast, the SSCH 256 chip sequence, or SSCH code, may bedifferent in each of the 15 slots of a radio frame and is used toidentify one of 64 possible scrambling code groups. In other words, eachradio frame of the SCH repeats a scrambling code group sequenceassociated with the respective transmitting cell. Each SSCH code istaken from an alphabet of 16 possible SSCH codes.

As part of the cell search, the UE first uses the PSCH to achieve slotsynchronization. In this regard, the UE correlates received samples ofthe received PSCH against the known PSCH 256 chip sequence (which is thesame for all slots) and, based on the location of the correlation peak,determines a slot reference time. Once the slot reference time isdetermined, the UE is slot synchronized and can determine when each slotstarts in a received radio frame.

After slot synchronization, the UE ceases processing of the PSCH andbegins processing the SSCH. In particular, the UE correlates theparticular sequence of 15 SSCH codes in a received radio frame againstknown sequences to achieve frame synchronization and to determine thescrambling code group of the cell. Identification of the scrambling codegroup then enables the UE to descramble all of the other downlinkchannels of the cell such as the Common Pilot Channel (CPICH)) necessaryfor UMTS voice/data communications to begin.

The now synchronized UE can then move to the active state and access theuplink Random Access Channel. The Random Access Channel (RACH) is anuplink transport channel. The RACH is always received from the entirecell. The RACH is characterized by a collision risk and by beingtransmitted using open loop power control. While on the RACH, the UEsends a long pilot sequence allowing the Node B to determine the UE'stime alignment. Once the UE has moved to the conversation stage of acall and is assigned to a DPCCH, pilot sequences transmitted by the UEare used to maintain the timing alignment. A total of 3 to 8 bits perslot are used for the mid-call uplink pilot sequences with 15 (0 to 14)slots available per frame. (As known to those of skill in the field ofwireless communications, the term “DPCCH” stands for Dedicated PhysicalControl Channel. The DPCCH is the physical channel on which thesignaling is transmitted, both on the uplink by the UE to the Node-Bbase transceiver station and on the downlink by the Node-B to the UE.)

The purpose of the time slot structure in UMTS is to provide a timingframework for determining when various events can occur. For example, auser's data rate can change for every frame, and power control commandsare sent every slot (thus giving WCDMA a power control rate of 1,500Hz). The data in WCDMA is modified by both spreading and scramblingcodes prior to transmission. De-scrambling and de-spreading the receivedspread spectrum signal requires accurate alignment of the received datato the de-scrambling/de-spreading codes. If the WLS is tasked mid-callvia the Iub or LMS, and therefore has no knowledge of the RACH burstsmade by the UE, and since the power control of the W-CDMA systemprecludes inexpensive broadcast channel monitoring, the WLS is presentedwith a problem in collecting uplink signals from the UE for locationpurposes. As explained below, the present invention addresses thisproblem.

SUMMARY

The following summary provides a high level overview of the inventivemethods and systems described herein. This summary is by no meansintended to cover all of the inventive subject matter described ingreater detail below, nor is it intended to limit the scope ofprotection of the claims appearing at the end of this specification.

The present invention allows for mid-call synchronizing of the WLSreceivers to the uplink frame and slot(s) used by themobile-to-be-located without downlink monitoring. The latency of themid-call synchronization can be shortened by giving the WLS additionalcoherency (known bit patterns), but a method has been found that may beused with no such information. In one illustrative example, in awireless location system, a method for determining frame and slot timinginformation for use in receiving an uplink signal from a user equipment(UE) device assigned to an uplink Dedicated Physical Control Channel(DPCCH) includes receiving signals in the uplink DPCCH at a locationmeasurement unit (LMU) of the WLS. The method also includes detecting apredefined bit pattern known to be present in a plurality of predefinedslots of the uplink DPCCH. Next, the frame and slot timing informationare determined for the uplink DPCCH based on the detected bit pattern.Finally, the frame and slot timing information is used for collectinguplink signals from the UE for use in location processing.

Other aspects of the inventive methods and systems are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following detailed description arebetter understood when read in conjunction with the appended drawings.For the purpose of illustrating the invention, there is shown in thedrawings exemplary constructions of the invention; however, theinvention is not limited to the specific methods and instrumentalitiesdisclosed. In the drawings:

FIG. 1 schematically depicts a UMTS Radio Access Network incorporating aU-TDOA or U-TDOA/AoA Wireless Location System as standardized by 3GPPwith improvements.

FIG. 2 depicts the frame and slot structure for UMTS W-CDMA uplinkchannels of interest.

FIG. 3 shows the UMTS pilot sequences available for mid-callsynchronization.

FIG. 4 illustrates the process where radio signals are monitored andtime alignment is obtained.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

We will now describe illustrative embodiments of the present invention.First, we provide an overview and then a more detailed description,including a discussion of the problem addressed by the invention and theinventive solutions.

Overview

Without access to the rough timing information provided to the UE viathe broadcast channel and without the fine timing developed from theuplink RACH pilot sequence, a WLS may be required to exploit amulti-frame, multi-slot pilot examination procedure to develop timing toallow reception of the uplink signaling from the mobile of interest forthe calculation of the uplink time difference of arrival. As describedin 3GPP specification 3GPP TS 25.211, “Physical channels and mapping oftransport channels onto physical channels. (FDD)”, the number of PilotBits included in the DPCCH can vary from 3 to 8 per slot. The pilotsequence also varies based on the slot format selected by the networkfor data bandwidth and quality of service purposes. If the slot formatis known to the WLS a priori, a multi-slot, multi-frame detectionprocedure can be used, taking advantage of the coherent detectionprocessing gain resulting from the known pilot sequence. This procedurewill allow the WLS to determine the uplink radio timing.

Once the frame and slot timing are known, capture of the uplink signalby the local LMU can occur and a TDOA and/or TDOA/AoA hybrid locationdeveloped using techniques described in other patents owned byTruePosition, Inc., the assignee of the present invention.

If the slot format and thus the number of pilot bits are not known tothe WLS, use of the full pilot bit sequence for coherent detection anddetermination of frame start cannot be accomplished. However, analternative method, where the slot format is not known to the WLS apriori, can be used. This alternative method relies on the fact that thefirst 3 bits for slots 0, 5, 6, and 9 do not change regardless of thenumber of Pilot Bits used per slot. By confining the examination of thepilot bits to first 3 bits, the WLS can take advantage of the coherentdetection and detect the slot format from these pilot bits.

We will now describe several exemplary environments in which the presentinvention may be deployed.

Overlay WLS Environments

FIG. 1 is illustrative of the wireless communications networks that thepresent invention functions within. While the following subsectionsdescribe exemplary implementations of the communications system as aUMTS, IS-95 and CDMA2000 cellular communication systems, the teachingsof the present invention are analogously also applicable to otherwideband, spread spectrum packet radio communication systems that areimplemented in other manners.

FIG. 1

FIG. 1 shows the architecture of an illustrative UMTS network referencemodel. UE (100)

The UMTS UE (User Equipment) 100 is the logical combination of the ME(Mobile Equipment) 101 and SIM/USIM (Subscriber Identity Module / UMTSSubscriber Identity Module) 102. The UE is the formal name for the UMTShandset or mobile.

ME (101)

The Mobile Equipment (ME) 101 is the hardware element of a mobilestation and comprises of keyboard, screen, radio, circuit boards andprocessors. The ME processors support both communications signalprocessing and processing of various UE-based services that may includea UE-based LCS Client application.

USIM (102)

The USIM (UMTS Subscriber Identity Module) 102, also referred to as aSIM card, is a programmable memory device what holds the usersubscription information to the UMTS mobile network. The USIM containsrelevant information that enables access onto the subscribed operator'snetwork and to UE-based services that may include a UE-based LCS Clientapplication.

Node B (105)

The Node B 105 is the function within the UMTS network that provides thephysical radio link between the UE 100 (User Equipment) and theland-side network. Along with the transmission and reception of dataacross the radio interface the Node B also applies the codes that arenecessary to describe channels in a W-CDMA system. The Node B suppliestiming information to UEs 100 over the Uu 105 interface. The Node Baccess the Uu interface via wired antenna feeds 104.

The UTRAN (UMTS Terrestrial Radio Access Network) comprises one or moreRNS (Radio Network Subsystem). Each RNS comprises one or more RNC 107and their supported Node B's 105. Each RNS control the allocation andthe release of specific radio resources to establish a connectionbetween a UE 100 and the UTRAN. A RNS is responsible for the resourcesand transmission/reception in a group of cells.

S-RNC (107)

When a RNC 107 (Radio Network Controller) has a logical RRC (RadioResource Control) connection with a UE (User Equipment) via the Node B105, it is known as the S-RNC 107 for that UE 100. The S-RNC 107 isresponsible for the user's mobility within the UTRAN network and is alsothe point of connection towards the CN (Core Network) 112. The S-RNC 107connects to the Node B via the 3GPP standardized Iub interface 106.

D-RNC (108)

When a UE 100 (User Equipment) in the connected state is handed onto acell associated with a different RNC it is said to have drifted. The RRC(Radio Resource Control) connection however still terminates with theS-RNC 107. In effect the D-RNC 108 acts as a switch, routing informationbetween the S-RNC 107 and the UE 100.

C-RNC

The Controlling Radio Network Controller is the RNC (Radio NetworkController) responsible for the configuration of a Node B. A UE (UserEquipment) accessing the system will send an access to a Node B, whichin turn will forward this message onto its CRNC. The C-RNC is nominallythe S-RNC.

Core Network (112)

The Core Network 112 provides the functions of mobility management,exchange services for call connection control signaling between the userequipment (UE) and external networks, and interworking functions betweenthe UTRAN radio access network and external packet and switched circuitnetworks. The Core Network also provides billing functionality, securityand access control management with external networks.

LMU (114)

The Location Measurement Unit (LMU) makes radio measurements to supportpositioning of UE. The LMU may be an overlay addition to the UMTSnetwork or may be integrated into the hardware and software of the NodeB. In the present example, the LMU receives the Um radio interface fordevelopment of TDOA and/or TDOA/AoA calculated location and velocityestimates. The LMU connects to cell site antenna or to the Node B via aradio coupler to the antenna feed 113.

Examples of a U-TDOA and U-TDOA/AOA LMU have been previously describedin U.S. Pat. No. 6,184,829, Calibration for a Wireless Location System;U.S. Pat. No. 6,266,013, Architecture for a Signal Collection System ina Wireless Location System; and U.S. Pat. No. 6,108,555, Enhanced TimeDifference Localization System, all owned by TruePosition andincorporated herein by reference.

SMLC (116)

The SMLC 116 is a logical functional entity implemented either aseparate network element (or distributed cluster of elements) orintegrated functionality in the RNC 107. The SMLC 116 contains thefunctionality required to support Location Based Services. The SMLC 113is the logical entity that provides the bridge between the wirelessnetwork and the location network (LMU 114, SMLC 116, and GMLC 119) bypossessing data concerning the geographical area as well as the radionetwork topology. The SMLC 116 manages the overall co-ordination andscheduling of LMU 114 resources required for the location of a mobile.It also calculates the final location, velocity, and altitude estimatesand estimates the achieved accuracy for each. In the present example,the SMLC 116 controls and interconnects a set of LMUs via packet dataconnections 115 for the purpose of obtaining radio interfacemeasurements to locate or help locate UE 100 in the geographical areathat its LMUs serve. The SMLC 116 contains U-TDOA, AoA and multipathmitigation algorithms for computing location, confidence interval,speed, altitude, and direction of travel. The SMLC 116 can alsodetermine which wireless phones to locate based upon triggering from theLink Monitoring System (LMS) 124 or requests from the 3GPP standardizedIupc interface 117 to an infrastructure vendor's Radio NetworkController (RNC) Station Controller 107.

GMLC (119)

The Gateway Mobile Location Center (GMLC) 119 is defined by 3GPPstandards as the clearinghouse for location records in a GSM/GPRS/UMTSnetwork. The GMLC 119 serves as a buffer between the tightly controlledSS7 network (the GSM-MAP and CAP networks) and the unsecure packet datanetworks such as the Internet. Authentication, access control,accounting, and authorization functions for location-based services arecommonly resident on or controlled by the GMLC 119. A Gateway MobileLocation Center (GMLC) is a server that contains the functionalityrequired to support LBS services as well the interworking, accesscontrol, authentication, subscriber profiles, security, administration,and accounting/billing functions. The GMLC also has the ability toaccess the GSM-MAP and CAP networks to discover subscriber identity,request and receive routing information, obtain low-accuracy UElocation, and to exert call control based on UE location. In any UMTSnetwork, there may be multiple GMLCs.

Network LCS Client (122)

A Network LCS Client 112 is the logical functional entity that makes arequest to the PLMN LCS server for the location information of one ormore than one target UEs. In the UTMS network depicted in FIG. 1, theLCS server is implemented as software and data on the GMLC 119 platform.This inclusion of the LCS server with the GMLC 119 is typical fordeployed systems. An LCS server comprises a number of location servicecomponents and bearers needed to serve the LCS clients. The LCS servershall provide a platform which will enable the support of location basedservices in parallel to other telecommunication services such as speech,data, messaging, other teleservices, user applications and supplementaryservices. The Network LCS client uses the Le interface 121 to access theGMLC. The network LCS client can communicate with the GMLC-based LCSserver 119 to request the immediate, periodic or deferred locationinformation for one or more target UEs within a specified set oflocation-related quality of service parameters if allowed by thesecurity and privacy protections provided by the GMLC-based LCS server119

Mobile LCS Client

The Mobile LCS Client is a software application residing in the ME 101of the UE 100 using the USIM 102 for non-volatile or portable datastorage. The mobile LCS Client may obtain location information via theGMLC 119 using the Le Interface 121 over a wireless data connection.

LMS

The LMS 133 provides passive monitoring of UMTS network interfaces suchas the Iub, Iur, Iu-CS and Iu-PS by means of passive probes (notpictured) reporting to a central server or server cluster. By monitoringthese interfaces, the LMS 133 may develop tasking and triggeringinformation allowing the SMLC 116 to provide autonomous, low-latencylocation estimates for pre-provisioned LBS applications. LMS 133developed triggering and tasking information is delivered to the SMLC116 via a generic data connection 123, normally TCP/IP based. The LMS133 is a modification to the Abis Monitoring System (AMS) described inU.S. Pat. No. 6,782,264, “Monitoring of Call Information in a WirelessLocation System” and later expanded in U.S. patent application Ser. No.11/150414, “Advanced Triggers for Location Based Service Applications ina Wireless Location System,” both incorporated herein by reference. TheLMS 133 may be incorporated as software into the Node B 105 or RNC 107,108 nodes of the UMTS system or deployed as an overlay network ofpassive probes.

Interfaces

The Uu interface 103 is the UMTS Air Interface as defined by 3GPP. Thisradio interface between the UTRAN (UMTS Terrestrial Radio AccessNetwork) and the UE (User Equipment) utilizes W-CDMA and eitherFrequency Division Duplexing (FDD) or Time Division Duplexing (TDD). TheUMTS radio interface is well described in 3GPP technical specifications25.201 and 45.201, both entitled; “Physical layer on the radio path;General description”. Specifics of the Uu radio interface as implementedin an FDD W-CDMA radio system are described in 3GPP TechnicalSpecification 25.213, “Spreading and modulation (FDD)”. Details anddescriptions of the physical and logical channels used in a FDD W-CDMAUMTS are located in 3GPP Technical Specification 25.211, “Physicalchannels and mapping of transport channels onto physical channels(FDD)”.

The Iub interface 106 is located in a UMTS radio network and is foundbetween the RNC (Radio Network Controller) 107 and the NodeB 105. TheIub interface is as defined in 3GPP TS 25.430, “UTRAN Iub Interface:general aspects and principles”.

The Iur 109 interconnects the UMTS Server or core RNC 70 with the DriftRNC 108 in the UMTS network. The Iur interface is standardized in 3GPPTechnical Specification 25.420, “UTRAN Iur Interface: General Aspectsand Principles”

The Iu-CS (Circuit Switched) interface 110 connects the UMTS RNC 107with the circuit switched communications oriented portion of the CoreNetwork 112.

The Iu-PS (Packet Switched) interface 111 connects the UMTS RNC 107 withthe packet switched communications oriented portion of the Core Network112.

The Iupc 117 interconnects the UMTS RNC 70 with the SMLC (also calledthe SAS) in the UMTS network for location estimation generation. TheIupc interface is introduced in 3GPP Technical Specification 25.450,“UTRAN Iupc interface general aspects and principles”.

The E5+ interface 118 is a modification of the E5 interface defined inthe Joint ANSI/ETSI Standard 036 for North American E9-1-1. The E5+interface 118 connects the SMLC 116 and GMLC 119 nodes directly,allowing for push operations when LMS 114 triggers are used by thewireless location system with either network acquired information(cell-ID, NMR, TA, etc) or via TDOA and/or AoA (angle of arrival)performed by the LMU's 114 specialized receivers.

The Le interface 121 is an IP-based XML interface originally developedby the Location Interoperability Forum (LIF) and then later standardizedby the 3rd Generation Partnership Program (3GPP) for GSM (GERAN) andUMTS (UTRAN). The Location-based services (LBS) client 122 is also knownas a LCS (Location Services). The LBS and LCS services resident on theLCS Client 122 are software applications, data stores, and servicesuniquely enabled to use the location of a mobile device.

Mid-call Synchronization for U-TDOA & AOA Location

FIG. 2 shows the arrangement of frame 200 and slots 201 used in the UMTSUu radio interface for transmission of the uplink Dedicated PhysicalControl Channel (DPCCH) 202 and Dedicated Physical Data Channel (DPDCH)203. The UE originating data transmitted within the DPCCH 202 and DPCH203 are bit streams that are I/Q multiplexed prior to scrambling,spreading and transmission from the UE.

The uplink DPCCH 202 (also abbreviated as UL-DPCCH) is used to carry theDCH (Dedicated Channel) transport channel. The uplink DPCCH 202 is alsoused to carry control information generated at the physical layer (Layer1). It is the DPCCH 202 that carries the 3-8 pilot bits 204 per slotthat are used by the multi-frame, multi-slot synchronization operation.

The DPDCH 203 (also abbreviated as UL-DPDCH) is UMTS uplink dedicatedphysical channel. The uplink DPDCH 203 is used to carry the DCH(Dedicated Channel) transport channel. There may be zero, one, orseveral uplink DPDCH 203 on each radio link depending on data throughputand quality of service requirements.

As is well-known to those skilled in the art, in the UMTS system, in theDPCCH channel, the spreading factor is always set to 256. Thus, eachdata bit results in 256 chips. If no bits are known, then for each bitperiod, a 256-chip sequence representing a possible ‘0’, and another 256chip sequence representing a ‘1’, can be correlated. This can then bedone for N different bits, which then leaves 2^(N) possible combinationsof bits, from which the correct one is chosen. This process is verycomputationally intensive and provides limited coherent processing gain.While techniques using massively parallel, spreading tree correlatorsare possible, a simpler and currently more economical method exists.

Nominal Case: WLS Given Pilot Sequences

In the nominal case, the RNC using the Iupc interface or LMS via itsdata link to the SMLC would provide the WLS with details of the UE to belocated including physical radio channel related information. Where theWLS has been given the frame, slot and pilot sequences (or simply theN_(pilot) bit count for the slots of interest), and N consecutive bitsare known (the pilot sequence), then 256*N consecutive chips can be usedto perform a coherent correlation over the N bit periods. Thissignificantly reduces the required processing, since multiple bitpossibilities do not need to be considered, and, more importantly,provides an additional 10*Log(N) dB of processing gain, and eliminatesthe need for the correct bit sequence selection (and loss of sensitivityresulting from multiple possibilities).

WLS Not Given Pilot Sequences

In the case where the WLS has not been given the pilot sequences, thetechnique based on the common pilot pattern of three bits may be used.As shown in FIG. 3 (see Tables 3 and 4), the bit pattern “1-1-1” inslots 0, 5, 6, and 9 (indicated by arrows) does not change regardless ofthe number of Pilot Bits used per slot. With 3 consecutive bits knownfor the 4 slots, then 768 (256*4) consecutive chips can be used toperform a coherent correlation over the 3-bit periods. This coherentdetection provides an additional 10*Log(3) dB of processing gain, andeliminates or avoids the need for a priori knowledge of the pilot bitsequences. Since the 3-bit sequence occurs in slots 0, 5, 6, and 9within the 10 ms frame, the pattern detection allows for computation ofboth frame start and slot start.

Once the LMU has been tasked and the timing alignment developed, the LMUmay collect the radio signal for U-TDOA location estimation and FDOAspeed and heading estimation as described, e.g., in U.S. Pat. No.5,327,144, Jul. 5, 1994, “Cellular Telephone Location System”; and U.S.Pat. No. 6,047,192, Apr. 4, 2000, “Robust Efficient LocalizationSystem,” both of which are hereby incorporated by reference. U-TDOA is astandardized UMTS location technology, please see 3GPP TS 25.305, “Stage2 functional specification of User Equipment (UE) positioning in UTRAN”and 3GPP TS 22.071, “Location Services (LCS); Service description; Stage1”.

FIG. 3 includes a modification to Table 3, “Pilot bit patterns foruplink DPCCH with N_(pilot)=3, 4, 5, 6”, of the 3GPP specification 3GPPTS 25.211 section 5.2.1.1. FIG. 3 also includes a modification to Table4, “Pilot bit patterns for uplink DPCCH with N_(pilot)=7 and 8”, of the3GPP specification 3GPP TS 25.211 section 5.2.1.1. These tables togethershow the pilot bit pattern for each slot of the uplink DPCCH for allallowed values of the number of pilot bits (N_(pilot)). In the casewhere the number of pilot bits (N_(pilot)) is known by the WLS, the fullpilot sequence can be used in the determination of frame and slotposition. Where the number of pilot bits (N_(pilot)) is not known, thefirst three bits of slots 0, 5, 6, and 9 can still be used for thedetermination of frame and slot position.

FIG. 4 shows a procedure that may be used by the UMTS network toestablish synchronization with the UE prior to entering the active orconversation state. The present invention may be used by an overlay WLSwhen the UE is transmitting in the uplink direction, providing the DPCCHfor analysis. As shown, in this example, once the time alignment isdeveloped and the frame start and slot start times are known, the WLS'sLMU collects the UMTS radio signal for U-TDOA or U-TDOA/AoA locationestimation. In this example, the WLS performs the steps denoted 401,402, 403 and 404, i.e., it receives a tasked to locate a particular UEdevice assigned to a DPCCH, performs a multi-frame examination of theDPCCH, and then determines frame and slot timing for the DPCCH. Theframe and slot timing information permits the WLS, through its LMUs, tocollect uplink signals that can be used in location processing, usingknown U-TDOA and/or AoA methods. The location estimate can include thelatitude, longitude, and altitude of the UE. The location estimationprocessing uses frequency-difference-of-arrival to produce a speed andheading estimate. The WLS can optionally include error estimates orconfidence values for each produced datum (location, altitude, speed,and heading).

Conclusion

The true scope the present invention is not limited to the presentlypreferred embodiments disclosed herein. For example, the foregoingdisclosure of a presently preferred embodiment of a Wireless LocationSystem uses explanatory terms, such as Location Measurement Unit (LMU,Serving Mobile Location Center (SMLC), and the like, which should not beconstrued so as to limit the scope of protection of the followingclaims, or to otherwise imply that the inventive aspects of the WirelessLocation System are limited to the particular methods and apparatusdisclosed. Moreover, as will be understood by those skilled in the art,many of the inventive aspects disclosed herein may be applied inlocation systems that are not based on TDOA techniques. For example, theinvention is not limited to systems employing LMU's constructed anddeployed as described above. The LMU's and SMLC's, etc. are, in essence,programmable data collection and processing devices that could take avariety of forms without departing from the inventive concepts disclosedherein. Given the rapidly declining cost of digital signal processingand other processing functions, it is easily possible, for example, totransfer the processing for a particular function from one of thefunctional elements (such as the LMU) described herein to anotherfunctional element within the wireless communications network (such asthe BS or base station) without changing the inventive operation of thesystem. In many cases, the place of implementation (i.e., the functionalelement) described herein is merely a designer's preference and not ahard requirement. Accordingly, except as they may be expressly solimited, the scope of protection of the following claims is not intendedto be limited to the specific embodiments described above.

1. In a wireless location system for use in locating a mobiletransmitter, a method for determining frame and slot timing informationfor use in receiving an uplink signal from a user equipment (UE) deviceassigned to an uplink Dedicated Physical Control Channel (DPCCH),comprising: receiving uplink DPCCH signals in the uplink DPCCH at alocation measurement unit (LMU) of the WLS, said uplink DPCCH signalsbeing formatted into multiple frames and multiple slots per frame;detecting a predefined bit pattern known to be present in a plurality ofpredefined slots of the uplink DPCCH signals; examining the DPCCHsignals across multiple frames; determining the frame and slot timinginformation for the uplink DPCCH based on the detected bit pattern; andusing the frame and slot timing information, collecting uplink signalsfrom the UE for use in location processing.
 2. A method as recited inclaim 1, wherein the step of collecting uplink signals from the UEcomprises collecting uplink signals at a plurality of LMUs and usingsaid signals in time difference of arrival (TDOA) processing todetermine the location of the UE.
 3. A method as recited in claim 2,wherein said predefined bit pattern comprises the bit pattern “1-1-1”.4. A method as recited in claim 3, wherein said predefined slotscomprise slots 0, 5, 6, and 9 of a 10 millisecond (ms) frame.
 5. Amethod as recited in claim 4, wherein the WLS is overlaid on a UMTSwireless communications system, and wherein the UE to be locatedcomprises a wireless device communicating with said UMTS wirelesscommunications system.
 6. A wireless location system (WLS) for use inlocating a mobile transmitter, comprising: a network of locationmeasurement units (LMUs); and a processor configured to cause the systemto determine frame and slot timing information for use in receiving anuplink signal from a user equipment (UE) device assigned to an uplinkDedicated Physical Control Channel (DPCCH), including receiving signalsin the uplink DPCCH at a first LMU, said signals being formatted intomultiple frames and multiple slots per frame; detecting a predefined bitpattern known to be present in a plurality of predefined slots of theuplink DPCCH; examining the signals across multiple frames; determiningthe frame and slot timing information for the uplink DPCCH based on thedetected bit pattern; and using the frame and slot timing information tocollect uplink signals from the UE for use in location processing.
 7. Asystem as recited in claim 6, wherein the system is further configuredto collect uplink signals at a plurality of LMUs and use said signals intime difference of arrival (TDOA) processing to determine the locationof the UE.
 8. A system as recited in claim 7, wherein said predefinedbit pattern comprises the bit pattern “1-1-1”.
 9. A system as recited inclaim 8, wherein said predefined slots comprise slots 0, 5, 6, and 9 ofa 10 millisecond (ms) frame.
 10. A system as recited in claim 9, whereinthe WLS is overlaid on a UMTS wireless communications system, andwherein the UE to be located comprises a wireless device communicatingwith said UMTS wireless communications system.
 11. A method as recitedin claim 5 wherein said frame and slot timing information includes astart time for each frame and slot.
 12. A system as recited in claim 6wherein said frame and slot timing information includes a start time foreach frame and slot.
 13. A method for use by a wireless location system(WLS) in locating a user equipment (UE) device communicating via awireless communications system configured in accordance with UniversalMobile Telephone System (UMTS) technical specifications, comprising:receiving a task to locate said UE device mid-call, wherein said task isreceived following a process in which a Node B element of the UMTSsystem provides timing information via a broadcast channel; said UEperforms a cell search and accesses the UMTS system via a reverse accesschannel (RACH); the Node B element determines fine timing informationfrom a long pilot sequence; and the UE device converses with the UMTSsystem using a Dedicated Physical Control Channel (DPCCH) and aDedicated Physical Data Channel (DPDCH); receiving uplink DPCCH signalsfrom said UE device; detecting a predefined bit pattern known to bepresent in a plurality of predefined slots of the uplink DPCCH signals;performing a multi-frame examination of the DPCCH signals; determiningframe and slot timing information for the DPCCH, wherein said frame andslot timing information includes a start time for each frame and slot;collecting uplink signals from said UE device via a network of locationmeasurement units (LMUs); and determining the location of said UE deviceusing an uplink time difference of arrival (U-TDOA) location algorithm.14. A method as recited in claim 13 wherein the step of collectinguplink signals from the UE comprises collecting uplink signals at aplurality of LMUs and using said signals in time difference of arrival(TDOA) processing to determine the location of the UE.
 15. A method asrecited in claim 14 wherein said predefined bit pattern comprises thebit pattern “1-1-1”.
 16. A method as recited in claim 15 wherein saidpredefined slots comprise slots 0, 5, 6, and 9 of a 10 millisecond (ms)frame.
 17. A method as recited in claim 16 wherein the WLS is overlaidon a UMTS wireless communications system, and wherein the UE to belocated comprises a wireless device communicating with said UMTSwireless communications system.